v3.0-rc8

Recent changes:

• exposed --min-change value as a parameter. (was hardcoded at 200000)
• Issue #25, disable colors on non-tty
• added --no-send option. snapshots that are obsolete are now destroyed at the beginning of each dataset-transfer. this allows using --no-send as way to just thinout old snapshots. cleaned up stderr output when resuming.
• Added support for custom ssh client config
• Improved --rollback and incompatible snapshot detection. added --destroy-incompatible.